1. Field of the Invention
The present invention relates to a gauge for verifying the operation of an apparatus for inspecting leads of an electronic package, and more particularly to a gauge for verifying the calibration and inspection parameters of a lead inspection apparatus for ball grid arrays.
2. Description of Related Art
The electronics industry is continually decreasing the size of electronic devices while increasing the pin count of the devices in an effort to increase the density of electronic packaging. Surface mount technology provides the industry with the ability to continue this trend since surface mount leads can be located relatively close to each other, as compared to through-hole technology. Common surface mount devices include ball grid arrays (BGAs), quad flat packs (QFPs), flat packs, gull-wing devices and the like.
As the pin count increases and lead spacing decreases, controlling mechanical parameters of the component leads, such as lead coplanarity, lead pitch, missing leads, lead deformation and the like, is critical for ensuring proper electrical interconnections when the components are installed on a printed circuit board. Consequently, lead inspection systems are utilized throughout the industry, from component manufacturing to printed circuit board assembly, for inspecting the leads of electronic packages to ensure that they meet their dimensional requirements.
Conventional lead inspection systems include infrared systems, laser scanning systems, gray scale camera systems and the like. Lead inspection systems typically analyze one or more mechanical features of an electronic package using various algorithms that compare the results of detector readings to predetermined parameter limits to determine whether the component is an acceptable or an unacceptable device. The accuracy of inspection systems, however, may be affected by several factors, including system calibration and programmed inspection parameters, that can lead to improper component acceptances and/or rejections with the potential result that a defective component is installed on a board or a perfectly good component is discarded as defective.
Since system calibration may change or drift over a period of time, it is necessary that system calibration be periodically tested and adjusted to alleviate any potential problems due to an improperly calibrated system. Calibration methods used in the industry, which typically utilize optics, 3-D triangulation sensors and lasers, require a considerable amount of time to calibrate a system. Consequently, an inspection system may not be calibrated often enough to ensure accurate electronic component inspections. Additionally, these calibration methods typically cannot be performed on-line and require a production line shutdown.
Even when an inspection system is properly calibrated, electronic components may still be improperly rejected or accepted due to an inspection process error. For example, an operator typically programs an inspection system with one or more predetermined inspection parameters to define the allowable limits against which a particular electronic package is compared when evaluating whether to accept or reject the component. When a parameter limit is incorrectly programmed into the system, a component can be improperly accepted or rejected even though the system calibration is accurate. Such process errors generally will not be discovered by testing the calibration of the system.
A "golden" component, which is an actual electronic component with known dimensions, may be used to verify the calibration and inspection parameters of an inspection system. However, the dimensions of the golden component leads can become altered due to handling and its repeated use as a verification unit. Verification units have been developed that are more robust than a golden component so that the unit may be more likely to maintain its mechanical parameters even with repeated use and handling.
U.S. Pat. Nos. 5,489,832 and 5,477,138 to Erjavic et al. disclose verification units which resemble certain aspects of quad flat pack and plastic leaded chip carrier type packages and are used for testing the calibration of a lead inspection system for such electronic packages. These units, however, are not suitable for verifying the calibration or process parameters of a lead inspection system for a ball grid array (BGA), including plastic and ceramic BGAs, micro BGAs and similar chip on board components.
In view of the foregoing, it is an object of the present invention to provide an improved device and a method for verifying the calibration and process parameters of a lead inspection apparatus for inspecting predetermined mechanical parameters of a ball grid array and similar chip on board components, and a method of manufacturing the device.